Lecture 5
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34 Terms
What is a buffer?
A solution that resists changes in pH when certain amounts of acid or base are added.
What is a buffer made of?
A weak acid and its conjugate base, or a weak base and its conjugate acid.
How does a buffer resist changes in pH?
The weak acid can neutralize added base, while the conjugate base can neutralize added acid.
What is the Henderson–Hasselbalch equation used for?
It is used to calculate the pH of a buffer based on the pKa of the weak acid and the concentrations of the conjugate base and weak acid or vice versa
In the Henderson–Hasselbalch equation, what does HA represent?
The weak acid.
In the Henderson–Hasselbalch equation, what does A− represent?
The conjugate base of
What is protonation?
The addition/gain of a proton (H+).
What is deprotonation?
The removal/loss of a proton (H+).
What generally happens to molecules at low pH? pH < pKa
They tend to become more protonated because there is more H+ available.
What generally happens to molecules at high pH? pH > pKa
They tend to become more deprotonated because there is less H+ available.
What are the protonated and deprotonated forms of an amino group?
Protonated: NH3+ (+1)
Deprotonated: NH2 (0)
What are the protonated and deprotonated forms of a carboxyl group?
Protonated: COOH (0)
Deprotonated: COO− (-1)
What is Physiological pH?
Physiological pH = ~7.4
What happens if animal cell pH drops below 6.8 or rises above 7.8?
Cells can suffer irreparable damage and die.
What is acidosis?
A condition in which the body's fluids become too acidic, resulting in a decrease in pH.
What is alkalosis?
A condition in which the body's fluids become too alkaline, resulting in an increase in pH.
What is the buffer system of the body?
The Carbonate Bicarbonate buffer system
What is a zwitterion?
A molecule that contains both a positive and negative charge but has an overall net charge of zero.
What does a typical amino acid look like as a zwitterion?
NH3+−CHR−COO− (Isoelectric charge = 0)
What is a polypeptide?
A chain of amino acids linked together by peptide bonds.
What bond links amino acids together in a polypeptide?
A peptide bond.
What process occurs when a peptide bond is formed?
A condensation (dehydration) reaction occurs.
Why is it called a dehydration reaction?
Because H₂O is removed during the reaction
What parts of the amino acids are removed to form H₂O?
An OH from the carboxyl group and an H from the amino group combine to form H₂O.
What process breaks a peptide bond?
Hydrolysis
What four groups are attached to the α-carbon in a typical amino acid?
Amino group (NH3+)
Carboxyl group (COO−)
Hydrogen (H)
R group (side chain)
What is the geometry around the α-carbon?
Tetrahedral geometry.
What makes α-carbon chiral?
An α-carbon is chiral when it is attached to four different groups.
Which amino acid is an exception and is not chiral?
Glycine, because its R group is another hydrogen.
What are the two possible arrangements of a chiral amino acid?
They are non-superimposable mirror images, called enantiomers.
What do L and D describe?
They describe the configuration (3D arrangement) of an amino acid relative to a reference molecule called glyceraldehyde.
Which configuration do amino acids found in proteins almost always have?
L-amino acids.
Are all L-amino acids S?
Almost all are S, but not all.
Is life stereospecific?
Stereospecific